1. Field of the Invention
The present invention relates in general to a cell for use in a solid polymer electrolyte fuel cell that employs a solid polymer electrolyte membrane, and more particular to a cell for a solid polymer electrolyte fuel cell of novel construction that affords a high level of gas flow path sealing functionality within the cell by means of a simple construction.
2. Description of the Related Art
As is well known, solid polymer electrolyte fuel cells are able to produce electrical power by means of an electrochemical reaction when supplied with oxygen (air) as an oxidant and hydrogen as a fuel, these being supplied onto the surfaces of a pair of catalyst electrodes superposed against either face of an electrolyte which is a solid polymer electrolyte membrane, such as a solid ion exchange membrane or the like.
In solid polymer electrolyte fuel batteries, it is important that there be consistent supply of oxygen and hydrogen onto the surfaces of the catalyst electrodes in order to consistently and efficient produce the intended voltage. It is also important for the appropriate temperature to be maintained.
Accordingly, there is typically employed a cell of a structure wherein a membrane/electrode assembly (MEA) composed of a breathable porous membrane oxidant electrode and a fuel electrode disposed on either side of the solid polymer electrolyte membrane is assembled with a first separator superposed against the oxidant electrode face thereof and a second separator superposed against the fuel electrode face thereof. A plurality of such unit cells are stacked and electrically connected directly to produce the desired voltage.
An oxidant gas flow passage is formed by means of covering with the oxidant electrode a recess disposed on the first separator, and fuel gas flow passage is formed by means of covering with the fuel electrode a recess disposed on the second separator. A coolant flow passage is formed by a recess disposed in a secondary face of the first separator or second separator on the back side from a primary face which is superposed against the electrode, by covering the recess with the secondary face of another adjacent cell.
At respective peripheral edges of stacked unit cells, there are formed perforating therethrough in the stacking direction an oxidant gas inlet and an oxidant gas outlet, a fuel gas inlet and a fuel gas outlet, and a coolant inlet and a coolant outlet. Oxidant gas, fuel gas, and coolant supplied through these inlets and outlets are circulated the aforementioned oxidant gas flow passages, fuel gas flow passages, and coolant flow passages of the unit cells, and are discharged from the outlets (as taught in JP-A-2002-83610, for example).
In such a solid polymer electrolyte fuel cell, since the power generating capability of a single unit cell is low, on the order to 0.7 V, there is employed a construction in which a multitude of cells are stacked together and electrically connected directly in order to obtain the desired power generating capability. However, there it the problem that when large numbers of cells are stacked, the overall size of the fuel cell becomes rather large.
In order to reduce overall size a fuel cell, it would be conceivable to make thinner the first and second separators, whose dimensional limitations in terms of performance are less than those of the membrane/electrode assembly. However, where the first and second separators are made thinner, rigidity of the components is lower, and thus during transport subsequent to manufacture or during assembly, there is a risk that the separators may become deformed. If a separator becomes deformed, in the assembled cell there is an attendant risk of diminished sealing of the gas flow zone formed between the juxtaposed faces of the membrane/electrode assembly and the separator, creating the possibility of diminished performance and reliability.
In recent years in particular, there has been a trend towards using higher gas pressure levels within flow passages, for the purpose of rapidly expelling the water that forms within the gas flow passages to prevent it from collecting, as well as making the electrochemical reaction more efficient. Thus, it is recognized that it is extremely important to ensure separator rigidity. Accordingly, it was very difficult to design a more compact fuel cell by means of reducing separator thickness.